1. Field of the Invention
The present invention relates to plasma-producing gases for the plasma projection of metallic oxides.
2. Description of Prior Art
Plasma projection is a process of coating under heat which consists in introducing a particulate material into a plasma jet wherein the particles are melted and accelerated before being flattened against the surface of the material to be coated. The main applications are the production of anti-wear, anti-corrosion, anti-friction deposits or deposits which act as heat and/or electrical barriers.
The operation is carried out in the presence of ambient air (APS process), or in an enclosure containing a neutral gas (LPPS process at low pressure, IPS under controlled atmosphere, ATC under controlled atmosphere and temperature).
The control of the parameters during plasma projection is difficult, since the quality and the speed of deposit depend largely on the molten state of the particles upon impact. It is thus necessary to entirely melt the particles but at the same time they should be prevented from being vaporised. It is therefore necessary to simultaneously control the heat conductivity of the plasma jet and the time of residence of the particles in the latter, this time, in particular, being a function of the length of the plasma jet.
Plasma producing gases are already known which consist of a binary mixture of argon and hydrogen (typically 75 to 95 volume % of argon and 5 to 25 volume % of hydrogen), as well as argon and helium.
The present invention aims at proposing a plasma producing gas enabling to obtain a plasma jet which is more homogeneous for a longer length of the jet, i.e. a jet presenting a less degraded transverse heat gradient on the edges of the jet and this, on a more substantial length at the outlet of the torch.